Hybridoma antibodies were produced (3 clones) against surface protein(s) of eosinophils and against urinary low molecular weight proteins and post-gamma globulin. The "eosinophil" antibodies are cytotoxic and their specificity is being established. Bladder tumors were induced in rats by chemical carcinogens and the urines and sera are being tested for levels of rat beta 2-microglobulin (beta 2 m) to test the hypothesis that tumor antigens may have similar over-all chemical structure as histocompatibility antigens, namely they also contain beta 2 m as an integral part of their structure. The beta 2 m-blocking test ("bb test") using turkey anti-beta 2m was thoroughly tested and its practical importance became evident. Its use for routine B-cell antigen testing (DR-antigens) enhances the "specificity" of this type of histocompatibility testing. Cow and horse beta 2-microglobulins were isolated and production of turkey anti-bovine and equine beta 2 m was initiated. These reagents will be very useful in veterinary histocompatibility testing. Urinary post-gamma globulin was studied further and a higher molecular form of this protein was discovered in serum and urine. Isolation, characterization and the mode of its degradation is studied. The presence of this protein in cell membranes in various tissue is being investigated. Search for the biological role of beta 2-microglobulin in embryology is pursued with the aid of antibodies against chicken beta 2 m.